For the preparation of 1-(alkoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxanes, several means are known in the art, but suffer from problems. For example, U.S. Pat. No. 4,871,827 (JP-A 62-207383), U.S. Pat. No. 4,772,675, JP-A 1-197509, U.S. Pat. No. 5,276,123 (JP-A 6-172536), JP-A 6-166810, JP-A 7-70551, JP-A 9-12709, JP-A 9-309889, JP-A 2000-256374, and JP-A 2001-348429 disclose methods for preparing 1-(alkoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxanes by reacting vinyl-containing alkoxysilanes with 1,1,3,3-tetramethyldisiloxane under varying conditions and in the presence of platinum compounds as the reaction catalyst. More specifically, in U.S. Pat. No. 4,871,827 to Klosowski et al., a reactor is charged with vinyltrimethoxysilane (which is a vinyl-containing alkoxysilane), 1,1,3,3-tetramethyldisiloxane in a 2-times molar amount relative to moles of vinyltrimethoxysilane, and a platinum catalyst all in their entirety, whereupon reaction is effected to form 1-(trimethoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane (which is a 1-(alkoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane). It is noted that for the synthesis of 1-(alkoxysilyl)ethyl-1,1,3,3-tetramethyl-disiloxane, the theoretically necessary amount of 1,1,3,3-tetramethyldisiloxane is an equimolar amount relative to a molar amount of the vinyl-containing alkoxysilane. However, since 1,1,3,3-tetramethyldisiloxane has a chemical structure that possesses per molecular two sites (H—Si groups) capable of addition reaction with vinyl groups, there is a likelihood that a by-product forms in which the vinyl-containing alkoxysilane adds at both the sites. To alleviate this problem, Klosowski patent recommends to use a large excess of 1,1,3,3-tetramethyldisiloxane, which is as large as 2 to 4 times the molar amount of the vinyl-containing alkoxysilane. Smaller amounts of 1 to 2 times molarity are unsatisfactory because more by-product is formed, resulting in a substantial drop of yield.
However, even the mixing conditions recommended by Klosowski patent are still insufficient because the percent yield is very low. For instance, in the example of Klosowski patent where reaction is performed using vinyltrimethoxysilane and 1,1,3,3-tetramethyldisiloxane in a molar ratio of 1/2, the yield of 1-(trimethoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane is about 80% relative to the vinyltrimethoxysilane and merely about 40% relative to the 1,1,3,3-tetramethyldisiloxane. The means of using a large molar excess of 1,1,3,3-tetramethyldisiloxane relative to the vinyl-containing alkoxysilane manifests an economical disadvantage because the cost of 1,1,3,3-tetramethyl-disiloxane becomes increased and the percent yield per unit volume is inevitably low. For the preparation of 1-(alkoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxanes, it would then be desirable to select a set of reaction conditions that eliminates a need for a large molar excess of 1,1,3,3-tetramethyldisiloxane relative to the vinyl-containing alkoxysilane and achieves higher yields than in the prior art methods.
Under the circumstances, Crivello et al., Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 31, 3121-32 (1993), report that when equimolar amounts of a vinyl-containing alkoxysilane (e.g., vinyltrimethoxysilane) and 1,1,3,3-tetramethyldisiloxane are reacted in the presence of RhCl(PPh3)3 as a reaction catalyst, a 1-(alkoxysilyl)-ethyl-1,1,3,3-tetramethyldisiloxane is prepared in higher yields than the process conducted in the presence of platinum catalysts. Specifically, a reactor is charged with RhCl(PPh3)3 on a polymer carrier, and equimolar amounts of 1,1,3,3-tetramethyldisiloxane and vinyltrimethoxysilane, and toluene all in their entirety, whereupon the contents are heated at 80° C. and reacted for 16 hours. The toluene and excessive reactants are removed from the reaction mixture, which is then distilled, collecting 1-(trimethoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane in a yield of 85.6%. Although this method advantageously eliminates the need for a large molar excess of 1,1,3,3-tetramethyldisiloxane relative to the vinyl-containing alkoxysilane, the yield of 1-(alkoxysilyl)-ethyl-1,1,3,3-tetramethyldisiloxane is still insufficient. There still exists a need for a method capable of offering higher yields.
It is described in the report of Crivello that the 1-(trimethoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane product is a mixture of two isomers resulting from addition of H—Si groups to a CH2=CH—Si group, that is, a compound having a —Si(CH2)2Si— linkage, i.e., 1-[2-(trimethoxysilyl)-ethyl]-1,1,3,3-tetramethyldisiloxane (referred to as beta-adduct) and a compound having a —SiCH(CH3)Si— linkage, i.e., 1-[1-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyl-disiloxane (referred to as alpha-adduct), and that the ratio of isomers, i.e., alpha-adduct/beta-adduct ratio is 1/2 (=33/67). As to the reaction in the presence of platinum catalysts, it is described in U.S. Pat. No. 5,276,123 that the 1-(trimethoxysilyl)ethyl-1,1,3,3-tetramethyldisiloxane product contains not only a compound having a —Si(CH2)2Si—linkage, i.e., 1-[2-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyldisiloxane (beta-adduct), but also an isomeric compound having a —SiCH(CH3)Si— linkage, i.e., 1-[1-(trimethoxysilyl)ethyl]-1,1,3,3-tetramethyldisiloxane (alpha-adduct) and that the product is a mixture of isomers in an alpha-adduct/beta-adduct ratio of 1/2 (=33/67).
It is known that the hydrolysis rate of an alkoxysilyl group becomes slower as the alkyl substituent bonded to the alkoxysilyl group is bulkier so that more steric hindrance is provided during reaction. Then, as compared with the beta-adduct having primary carbon bonded to its alkoxysilyl group, the alpha-adduct having secondary carbon bonded has a low hydrolysis rate. Since higher hydrolysis rates are preferred in the area of application where the relevant compounds are used, there exists a need for a method capable of affording a less amount of alpha-adduct isomer, namely a high selectivity.